1. Field of the Art
The invention is directed to a corneal surgery apparatus. In particular, this invention is a microkeratome instrument for use in refractive surgery.
2. Discussion of Background and Prior Art
Correctable conditions of the optical system in the eye are known. Myopia (nearsightedness) is a condition where the visual images come to focus in front of the retina of the eye resulting in defective vision of distant objects. Hyperopia (farsightedness) is a condition in which visual images come to focus behind the retina of the eye and vision is better for distant objects than for near objects. Astigmatism is a condition in which light rays from a point fails to meet in a single focal point, resulting in a blurred and imperfect image. In the human eye this defect of vision due to astigmatism is typically due to a corneal irregularity.
Refractive surgery is a known method of treating myopia, hyperopia, astigmatism, and certain corneal abnormalities. This process involves reshaping various layers of the cornea to change the refractive surface thereof. Numerous methods of refractive surgery have been developed, including radial keratotomy (where radial slits are cut into the cornea to correct myopia), automated lamellar keratoplasty ("ALK", where a first flap is created in the upper layer of the cornea with a microkeratome, then additional corneal tissue is removed to correct vision), laser photorefractive keratectomy ("PRK"), among other methods. Presently, LASIK (the acronym for "laser assisted in situ keratomileusis"), has gained popularity. In the LASIK procedure, an excimer laser is used to reshape the cornea after a thin layer of the cornea (a corneal flap) is raised in a procedure called a keratectomy. The excimer laser is used to ablate selective areas of the cornea under the incision, and thereafter the corneal flap is returned to its position, where it quickly heals.
A critical part of the LASIK procedure is cutting a generally circular flap on the top surface of the cornea, in a procedure called a keratectomy. The device used to do this is the microkeratome. Numerous different styles of microkeratomes are available. These prior art microkeratomes include an eye engaging portion that has an aspiration ring for securing the eye engaging portion to the eye, an applanate plane against which the cornea of the eye will press flat against, and a rapidly oscillating blade placed in close proximity to the applanate plane which are used slice the thin corneal flap. These different styles of microkeratomes are designed to be used with a speculum. After the flap is cut and folded back, an excimer laser is used to remove corneal tissue under the cut flap and reshape the cornea. Thereafter, the flap is laid back on top of the excised area. Use of a speculum during keratectomy can cause patient discomfort, and cause involuntary eye movement.
Furthermore, in some presently available microkeratomes, a head portion with the microkeratome blade must be carefully aligned with the eye engaging portion after the eye engaging portion is fitted to the eye which can be difficult to do.
In other microkeratome designs, the head portion is engaged with the eye engaging portion prior to placement on the eye. However, these designs tend to be bulky, reduce access to the surgical field, and can be awkward to place and remove from the eye.
The prior microkeratomes also either do not permit simple adjustment of the size of the uncut corneal flap or have bulky mechanisms.
A further inadequacy with some prior microkeratome designs is that their motorized handpieces are noisy, which further raises the anxiety level of the patient and can cause eye movement.
Other shortcomings with some presently available microkeratome include the quality of the corneal flap created during the keratectomy, the need to calibrate the depth of the cut (e.g. by adjusting the position of the applanata plane), and the difficulty in easily and consistently selecting the desired corneal flap thickness from procedure to procedure.
Yet a further shortcoming of present microkeratomes is that they can be troublesome to clean and sterilize. Indeed, disposable microkeratomes are now available to reduce sterilization downtime.
There accordingly remains a need for an improved microkeratome that addresses the above concerns.